Radiocarbon dating is the principal method for determining the age of carbon-bearing materials from the present to about 50,000 years ago.
The method takes advantage of the natural occurrence of a radioactive isotope of carbon (14C or "Carbon 14"). 14C is continuously produced in the upper atmosphere by the interaction of cosmic ray neutrons with 14N. The newly formed 14C rapidly oxidizes to carbon dioxide which is taken up by plants during photosynthesis, and also mixes with carbon dioxide dissolved in the hydrosphere.
From plants, 14C passes up the food chain to other organisms which will then assimilate into their structure 14C of equal proportion to that of atmospheric carbon dioxide. Once an organism dies, it ceases to participate in the flow of 14C from the atmosphere and the 14C in its structure is gradually lost by radioactive disintegration back to 14N. By measuring the amount of 14C in samples of ancient carbon compounds and comparing this with the amount in modern materials, it is possible to determine the time of cessation of carbon exchange with the atmosphere.
The radiocarbon lab at Geochron uses gas proportional counters to measure methane derived from relatively small samples. We also offer liquid scintillation analysis using an extra low background Quantulus 1220 for high precision measurements on benzene. Very small samples (less than 300 mg) are analyzed by accelerator mass spectrometry (AMS). We have subcontractor agreements with several AMS facilities around the world.
Materials suitable for radiocarbon dating include charcoal, wood and other plant matter, soils and sediments, shells, bone, carbonates, dissolved inorganic carbonate (DIC), methane and hydrocarbons, and food products. A table of optimum and minimum sample sizes is provided below. Please feel free to contact our lab staff to discuss the specific details of your samples.
Normal handling will not contaminate most sample types, however, samples should be protected from sources of extraneous carbon. Charcoal and wood samples should be wrapped in aluminum foil or heavy plastic and should not be wrapped in paper.
Contact us to discuss turn-around time and scheduling.
A 14C Sample Submission Form is available for download in several formats below. Please send a completed form for each sample or batch of samples.